The invention relates to the field of charged-particle systems, and in particular to a non-axisymmetric charged-particle system.
The generation, acceleration and transport of a high-brightness, space-charge-dominated, charged-particle (electron or ion) beam are the most challenging aspects in the design and operation of vacuum electron devices and particle accelerators. A beam is said to be space-charge-dominated if its self-electric and self-magnetic field energy is greater than its thermal energy. Because the beam brightness is proportional to the beam current and inversely proportional to the product of the beam cross-sectional area and the beam temperature, generating and maintaining a beam at a low temperature is most critical in the design of a high-brightness beam. If a beam is designed not to reside in an equilibrium state, a sizable exchange occurs between the field and mean-flow energy and thermal energy in the beam. When the beam is space-charge-dominated, the energy exchange results in an increase in the beam temperature (or degradation in the beam brightness) as it propagates.
If brightness degradation is not well contained, it can cause beam interception by radio-frequency (RF) structures in vacuum electron devices and particle accelerators, preventing them from operation, especially from high-duty operation. It can also make the beam from the accelerator unusable because of the difficulty of focusing the beam to a small spot size, as often required in accelerator applications.
The design of high-brightness, space-charge-dominated, charged-particle beams relies on equilibrium beam theories and computer modeling. Equilibrium beam theories provide the guideline and set certain design goals, whereas computer modeling provides detailed implementation in the design.
While some equilibrium states are known to exist, matching them between the continuous beam generation section and the continuous beam transport section has been a difficult task for beam designers and users, because none of the known equilibrium states for continuous beam generation can be perfectly matched into any of the known equilibrium states for continuous beam transport.
For example, the equilibrium state from the Pierce diode in round two dimensional (2D) geometry cannot be matched into a periodic quadrupole magnetic field to create a Kapachinskij-Vladimirskij (KV) beam equilibrium. A rectangular beam made by cutting off the ends of the equilibrium state from the Pierce diode in infinite, 2D slab geometry ruins the equilibrium state.
However, imperfection of beam matching in the beam system design yields the growth of beam temperature and the degradation of beam brightness as the beam propagates in an actual device.